I have been a fan of Galactic Civilizations since I first played it on OS/2 many years ago.
But I must say that Twilight of the Arnor is the best yet. The introduction of the new espionage system turned me off playing completely but in ToA the update has made the game enjoyable for me again.
Looking at the metaverse I see that my first game of Galciv II was posted the 14th of March 2006 and my last today on the 23rd of December 2008. I can't think of any other game besides Civilization 4 that I still play after such a long time and still find fun and challenging. The mostly excellent expansion packs are probably one of the main reasons.
So thanks a lot and Merry Christmas!